nss_files: Add generic code for set*ent, end*ent and file open

This reduces RSS usage if nss_files is not actually used, and can
be used later to make NSS data thread-specific.  It also results in
a small code size reduction.

Before:

   text	   data	    bss	    dec	    hex	filename
   2288	      0	     72	   2360	    938	nss/files-alias.os
   1807	      0	     72	   1879	    757	nss/files-ethers.os
   1371	      0	     72	   1443	    5a3	nss/files-grp.os
   6246	      0	     72	   6318	   18ae	nss/files-hosts.os
    869	      0	      0	    869	    365	nss/files-initgroups.os
    666	      0	      0	    666	    29a	nss/files-init.os
   1934	      0	      0	   1934	    78e	nss/files-netgrp.os
   2353	      0	     72	   2425	    979	nss/files-network.os
   2130	      0	     72	   2202	    89a	nss/files-proto.os
   1372	      0	     72	   1444	    5a4	nss/files-pwd.os
   2124	      0	     72	   2196	    894	nss/files-rpc.os
   2265	      0	     72	   2337	    921	nss/files-service.os
   1125	      0	     72	   1197	    4ad	nss/files-sgrp.os
   1124	      0	     72	   1196	    4ac	nss/files-spwd.os

After:

   text	   data	    bss	    dec	    hex	filename
   2040	      0	      0	   2040	    7f8	nss/files-alias.os
   1599	      0	      0	   1599	    63f	nss/files-ethers.os
   1155	      0	      0	   1155	    483	nss/files-grp.os
   6010	      0	      0	   6010	   177a	nss/files-hosts.os
    869	      0	      0	    869	    365	nss/files-initgroups.os
    666	      0	      0	    666	    29a	nss/files-init.os
   1934	      0	      0	   1934	    78e	nss/files-netgrp.os
   2129	      0	      0	   2129	    851	nss/files-network.os
   1914	      0	      0	   1914	    77a	nss/files-proto.os
   1156	      0	      0	   1156	    484	nss/files-pwd.os
   1908	      0	      0	   1908	    774	nss/files-rpc.os
   2057	      0	      0	   2057	    809	nss/files-service.os
    909	      0	      0	    909	    38d	nss/files-sgrp.os
    908	      0	      0	    908	    38c	nss/files-spwd.os
   1090	      0	      8	   1098	    44a	nss/nss_files_data.os

27674 code bytes before, 26344 code bytes after, so it is an overall
win despite the extra initialization code.

Reviewed-by: Adhemerval Zanella  <adhemerval.zanella@linaro.org>

1 files changed, 161 insertions, 0 deletions

diff --git a/nss/nss_files_data.c b/nss/nss_files_data.c
new file mode 100644
index 0000000000..80fbfe5fff
--- /dev/null
+++ b/nss/nss_files_data.c
@@ -0,0 +1,161 @@
+/* Returns a pointer to the global nss_files data structure.
+   Copyright (C) 2021 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <https://www.gnu.org/licenses/>.  */
+
+#include <nss_files.h>
+
+#include <allocate_once.h>
+#include <errno.h>
+#include <netdb.h>
+#include <nss.h>
+#include <stdlib.h>
+
+/* This collects all per file-data.   */
+struct nss_files_data
+{
+  struct nss_files_per_file_data files[nss_file_count];
+};
+
+/* For use with allocate_once.  */
+static void *nss_files_global;
+static void *
+nss_files_global_allocate (void *closure)
+{
+  struct nss_files_data *result = malloc (sizeof (*result));
+  if (result != NULL)
+    {
+      for (int i = 0; i < nss_file_count; ++i)
+        {
+          result->files[i].stream = NULL;
+          __libc_lock_init (result->files[i].lock);
+        }
+    }
+  return result;
+}
+/* Like __nss_files_data_open, but does not perform the open call.  */
+static enum nss_status
+__nss_files_data_get (struct nss_files_per_file_data **pdata,
+                      enum nss_files_file file, int *errnop, int *herrnop)
+{
+  struct nss_files_data *data = allocate_once (&nss_files_global,
+                                               nss_files_global_allocate,
+                                               NULL, NULL);
+  if (data == NULL)
+    {
+      if (errnop != NULL)
+        *errnop = errno;
+      if (herrnop != NULL)
+        {
+          __set_h_errno (NETDB_INTERNAL);
+          *herrnop = NETDB_INTERNAL;
+        }
+      return NSS_STATUS_TRYAGAIN;
+    }
+
+  *pdata = &data->files[file];
+  __libc_lock_lock ((*pdata)->lock);
+  return NSS_STATUS_SUCCESS;
+}
+
+/* Helper function for opening the backing file at PATH.  */
+static enum nss_status
+__nss_files_data_internal_open (struct nss_files_per_file_data *data,
+                                const char *path)
+{
+  enum nss_status status = NSS_STATUS_SUCCESS;
+
+  if (data->stream == NULL)
+    {
+      data->stream = __nss_files_fopen (path);
+
+      if (data->stream == NULL)
+        status = errno == EAGAIN ? NSS_STATUS_TRYAGAIN : NSS_STATUS_UNAVAIL;
+    }
+
+  return status;
+}
+
+
+enum nss_status
+__nss_files_data_open (struct nss_files_per_file_data **pdata,
+                       enum nss_files_file file, const char *path,
+                       int *errnop, int *herrnop)
+{
+  enum nss_status status = __nss_files_data_get (pdata, file, errnop, herrnop);
+  if (status != NSS_STATUS_SUCCESS)
+    return status;
+
+  /* Be prepared that the set*ent function was not called before.  */
+  if ((*pdata)->stream == NULL)
+    {
+      int saved_errno = errno;
+      status = __nss_files_data_internal_open (*pdata, path);
+      __set_errno (saved_errno);
+      if (status != NSS_STATUS_SUCCESS)
+        __nss_files_data_put (*pdata);
+    }
+
+  return status;
+}
+
+libc_hidden_def (__nss_files_data_open)
+
+void
+__nss_files_data_put (struct nss_files_per_file_data *data)
+{
+  __libc_lock_unlock (data->lock);
+}
+libc_hidden_def (__nss_files_data_put)
+
+enum nss_status
+__nss_files_data_setent (enum nss_files_file file, const char *path)
+{
+  struct nss_files_per_file_data *data;
+  enum nss_status status = __nss_files_data_get (&data, file, NULL, NULL);
+  if (status != NSS_STATUS_SUCCESS)
+    return status;
+
+  if (data->stream == NULL)
+    status = __nss_files_data_internal_open (data, path);
+  else
+    rewind (data->stream);
+
+  __nss_files_data_put (data);
+  return status;
+}
+libc_hidden_def (__nss_files_data_setent)
+
+enum nss_status
+__nss_files_data_endent (enum nss_files_file file)
+{
+  /* No cleanup is necessary if not initialized.  */
+  struct nss_files_data *data = atomic_load_acquire (&nss_files_global);
+  if (data == NULL)
+    return NSS_STATUS_SUCCESS;
+
+  struct nss_files_per_file_data *fdata = &data->files[file];
+  __libc_lock_lock (fdata->lock);
+  if (fdata->stream != NULL)
+    {
+      fclose (fdata->stream);
+      fdata->stream = NULL;
+    }
+  __libc_lock_unlock (fdata->lock);
+
+  return NSS_STATUS_SUCCESS;
+}
+libc_hidden_def (__nss_files_data_endent)